Wiring connectors are often used to interconnect the lighting system wiring of a towing vehicle such as a truck to the lighting system wiring of a towed vehicle such as a boat trailer so that the turn signals, tail lights, and/or other lights on the towed vehicle are activated at the same time as the corresponding lights on the towing vehicle. For safety and proper operation, such connectors should always be grounded. Most connectors therefore have a ground terminal that is connected to a ground wire that is in turn bolted or otherwise electrically connected to a metal surface on the towed vehicle to provide such grounding. The ground terminal on the wiring connector plugs into a corresponding ground terminal on a mating wiring connector on the towing vehicle which is in turn connected to a ground wire that is bolted or otherwise electrically connected to a metal surface on the towing vehicle so as to ground the towing vehicle side of the wiring.
Improper ground connections are the most common cause of lighting problems in trailers and other towed vehicles. Grounding problems often occur when users simply fail to connect trailer ground wires to a ground source and/or when ground connections become loose or otherwise faulty over time due to vibration, rust, or debris buildup around the connections. Even though grounding problems are the chief cause of lighting connection problems in towed vehicles, many users don't recognize this, and instead improperly assume trailer wiring connectors are defective or broken when the lighting system on a towed vehicle doesn't work properly. Moreover, even when users suspect a grounding problem, poor or non-existent ground connections are sometimes difficult to locate and fix.